Unconditionally enable PGRP_PIPE on Linux (the kernel), regardless of
the kernel version in use on the build machine.

--- configure.ac.orig	2019-01-02 09:38:44.000000000 -0500
+++ configure.ac	2019-08-15 16:40:24.271758379 -0400
@@ -1108,10 +1108,7 @@
 solaris2*)	LOCAL_CFLAGS=-DSOLARIS ;;
 lynxos*)	LOCAL_CFLAGS=-DRECYCLES_PIDS ;;
 linux*)		LOCAL_LDFLAGS=-rdynamic		 # allow dynamic loading
-		case "`uname -r`" in
-		1.*|2.[[0123]]*)	: ;;
-		*)	AC_DEFINE(PGRP_PIPE) ;;
-		esac ;;
+		AC_DEFINE(PGRP_PIPE) ;;
 netbsd*|openbsd*)	LOCAL_CFLAGS="-DDEV_FD_STAT_BROKEN" ;;
 *qnx[[67]]*)	LOCAL_LIBS="-lncurses" ;;
 *qnx*)		LOCAL_CFLAGS="-Dqnx -F -3s" LOCAL_LDFLAGS="-3s" LOCAL_LIBS="-lunix -lncurses" ;;
--- configure.orig	2019-01-02 09:43:04.000000000 -0500
+++ configure	2019-08-15 16:41:44.440155912 -0400
@@ -16312,11 +16312,7 @@
 solaris2*)	LOCAL_CFLAGS=-DSOLARIS ;;
 lynxos*)	LOCAL_CFLAGS=-DRECYCLES_PIDS ;;
 linux*)		LOCAL_LDFLAGS=-rdynamic		 # allow dynamic loading
-		case "`uname -r`" in
-		1.*|2.[0123]*)	: ;;
-		*)	$as_echo "#define PGRP_PIPE 1" >>confdefs.h
- ;;
-		esac ;;
+		$as_echo "#define PGRP_PIPE 1" >>confdefs.h ;;
 netbsd*|openbsd*)	LOCAL_CFLAGS="-DDEV_FD_STAT_BROKEN" ;;
 *qnx[67]*)	LOCAL_LIBS="-lncurses" ;;
 *qnx*)		LOCAL_CFLAGS="-Dqnx -F -3s" LOCAL_LDFLAGS="-3s" LOCAL_LIBS="-lunix -lncurses" ;;
ckages/patches/kobodeluxe-paths.patch?id=0e42d239ecc7ef16ae6aa0df46ee4e1ff1b2ad3d'>tree</a><a href='/guix/commit/gnu/packages/patches/kobodeluxe-paths.patch?id=0e42d239ecc7ef16ae6aa0df46ee4e1ff1b2ad3d'>commit</a><a href='/guix/diff/gnu/packages/patches/kobodeluxe-paths.patch?id=0e42d239ecc7ef16ae6aa0df46ee4e1ff1b2ad3d'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/patches/kobodeluxe-paths.patch'>
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<div class='path'>path: <a href='/guix/log/?id=0e42d239ecc7ef16ae6aa0df46ee4e1ff1b2ad3d'>root</a>/<a href='/guix/log/gnu?id=0e42d239ecc7ef16ae6aa0df46ee4e1ff1b2ad3d'>gnu</a>/<a href='/guix/log/gnu/packages?id=0e42d239ecc7ef16ae6aa0df46ee4e1ff1b2ad3d'>packages</a>/<a href='/guix/log/gnu/packages/patches?id=0e42d239ecc7ef16ae6aa0df46ee4e1ff1b2ad3d'>patches</a>/<a href='/guix/log/gnu/packages/patches/kobodeluxe-paths.patch?id=0e42d239ecc7ef16ae6aa0df46ee4e1ff1b2ad3d'>kobodeluxe-paths.patch</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/patches/kobodeluxe-paths.patch?id=0e42d239ecc7ef16ae6aa0df46ee4e1ff1b2ad3d&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2016-10-18 20:35:01 -0500'>2016-10-18</span></td><td><a href='/guix/commit/gnu/packages/patches/kobodeluxe-paths.patch?id=3d1fe340db4f9d0d64d502fe2d2dbabf4ec811dd'>gnu: kobodeluxe: Indicate origin of kobodeluxe-paths.patch.</a><span class='msg-avail'>...</span></td><td>Christopher Allan Webber</td></tr>
<tr><td><span title='2016-10-18 20:23:03 -0500'>2016-10-18</span></td><td><a href='/guix/commit/gnu/packages/patches/kobodeluxe-paths.patch?id=a56145e1fa8c8c9cb866518efdeaaf4ad4017ba1'>gnu: Add kobodeluxe.</a><span class='msg-avail'>...</span></td><td>Stephen Webber</td></tr>